Osteoporosis directly affects 10 million Americans and another 34 million are osteopenic and at risk for developing osteoporosis. Bisphosphonate drugs, for example alendronic acid (ALN, Fosamax), can improve bone density and reduce fracture risk by slowing osteoclastic bone resorption; however, many of the existing anti-resorptive therapies are plagued with untoward side effects and limited duration of clinical benefits. New and improved strategies for therapeutic intervention in osteoporosis are needed, particularly with new treatments that safely promote anabolic bone growth. A dual therapy approach, addressing both resorption and formation of bone could also be helpful. Presently, there is only one FDA approved bone anabolic agent, Forteo (teriparatide), that confers significant clinical benefits in osteoporosis, but its use is severely restricted due to safety concerns. Multipotent mesenchymal stem cells (MSCs) are precursors of a variety of cell types, including osteoblasts and adipocytes. Formation of new bone is driven by osteoblastic differentiation of MSCs, a process that can be thrown off balance by age, lifestyle factors and hormonal changes that occur with menopause. Parhami et al. discovered that specific oxysterols induce osteogenesis when applied to MSCs while inhibiting their adipogenesis. The most promising proprietary semi-synthetic oxysterol to date, OXY133, displays increased potency for osteogenic differentiation in vitro, including in primary rat, rabbit, and human MSCs, and it stimulates robust localized bone formation in vivo in rat and rabbit spine fusion and crania and femoral defect models. During SBIR Phase I research, we have begun evaluating drug conjugates of osteo- anabolic Oxy133 and Alendronate (ALN), a well-established anti-resorptive drug that also serves as a bone- targeting agent. We have worked out methods for chemical conjugation and characterized biophysical and biological properties of the resulting conjugates. Oxy133-ALN conjugates display strong in vitro binding to bone mineral and stimulate Hedgehog (Hh) pathway signaling and osteogenesis in MSCs. In this application, we propose to further develop Oxy133-ALN conjugates as potential dual therapy agents for osteoporosis, stimulating bone formation by osteoblasts (function of Oxy133), and inhibiting bone resorption by osteoclasts (function of ALN). Expanding on our successful Phase I studies, we propose to perform Phase II studies as part of 3 Specific Aims: Aim 1: Development of scalable methods for the synthesis of Oxy133-ALN conjugates. Aim 2: Evaluation of the inhibition of osteoclastic bone-resorption by Oxy133-ALN conjugates and the possibility of a dual therapy. Aim3: Determination of Oxy133-ALN conjugate tissue distribution properties and evaluation of select Oxy133- ALN conjugates for efficacy in an OVX mouse model.